Majestic swans are disappearing from a historic British waterway, and detectives suspect that they are being stolen for food.

Witnesses told investigating officers that they saw a gang of five men attacking one of the snowy white birds with a nail-studded implement, according to a report in the UK’s The Daily Telegraph. And now a police team is probing whether four similar incidents are in fact linked, and the disappearances part of a larger conspiracy.

“The remains of five birds have been found. The evidence we have is that there is little left of the bodies and for the want of better words one of the birds was found in a bag done up like a turkey,” Police Constable Nick Willey told the London-based newspaper.

“Swans, like any wild bird, are protected by law so this is not only very cruel, but it’s also illegal.”

The first remains of a swan turned up on parkland by a Roman waterway in historic Lincoln, Lincolnshire, on Dec. 13, with further body parts reported just before Christmas and three more carcasses appearing thereafter.

Lincoln’s RSPCA branch is also investigating the case, according to local paper the Linconite, while residents have also created a Facebook page to collect information on any suspicious fatality. The city’s swans are iconic due to their centuries-old residence at Brayford Pool and surrounding rivers.